The formation of channel and shoal patterns in a schematic estuary is investigated using a 2-D depth-averaged numerical model based on a description of elementary flow and sediment transport processes. The schematisations apply to elongated inland estuaries, sandy, well-mixed and tide-dominated. The model results show how, due to non-linear interactions, a simple and regular pattern of initially grown perturbations merges to complex larger scale channel-shoal patterns. The emerging patterns are validated with field observations. The overall pattern agrees qualitatively with patterns observed in the Western Scheldt estuary, The Netherlands, and in the Patuxent River estuary, Virginia. Quantitative comparison of the number of channels and meander length scales with observations and with an analytical model gives reasonable accordance. Complementary to other research approaches, this model provides a tool to study the morphodynamic behaviour of channels and shoals in estuaries.